PSA approach for evaluation of external hazards as part of CNSC Fukushima action items

An abstract of a presentation at:
International Workshop on PSA of Natural External Hazards including Earthquakes
Prague, Czech Republic
June 17–19, 2013

Prepared by:
Michael Xu
Canadian Nuclear Safety Commission (CNSC)
Ottawa, Ontario, Canada

Abstract

This paper introduces the probabilistic safety assessment (PSA) approach that Canadian licensees adopted to address the Canadian Nuclear Safety Commission (CNSC) Fukushima Action Items (FAIs) with respect to external hazards evaluation. It also briefly discusses the differences between the requirements of CNSC FAIs and of the European Stress Test, and the current status of Canadian licensees' actions for completing these action items.

Following the Fukushima accident, a CNSC Fukushima Task Force (FTF) was created with the objective of reviewing the capability of nuclear power plants in Canada to withstand conditions similar to those that triggered the Fukushima accident. The task force created Fukushima FAIs, which requested all licensees to re-evaluate the site-specific external hazards of which the plant may be susceptible, and to evaluate if the current site-specific design protection for each of these external hazards is adequate.

In response to the requests of FAIs, all Canadian licensees chose to use site-specific PSAs to evaluate the external hazards. The approach includes screening analysis, bounding analysis and detailed analysis. As part of their compliance with the regulatory standard S-294, Probabilistic Safety Assessment for Nuclear Power Plants, licensees have submitted for CNSC acceptance the methodologies for hazards screening, seismic events evaluation, external floods, high winds and tornados. Seismic induced floods and fires are also considered part of the FAIs. All the submitted methodologies must follow international guidance and best practices.

There are some differences between CNSC FAIs and the European Stress Test in external hazards evaluation requirements. For example, the European Stress Test requires only seismic events and external flood, while CNSC FAIs require the consideration of all external hazards. The impact of external hazards on irradiated fuel bay (IFB) is also included in the scope of CNSC FAIs.

The progress in addressing CNSC FAIs differs for each respective nuclear power generating station. However, the expected completion date for all licensees is December 31, 2013.

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